1. Technical Field
This invention relates generally to filters, and more particularly to an improved filter element, a filter assembly in which it is used, and the fabrication methodology employed.
2. Background Information
Some filter elements include a porous member mounted on a support structure so that the porous member can be supported transversely to a flow of fluid in order to trap particulate matter as the fluid flows through it. We can use the filter element alone for such purposes as filtering particulate matter from water as the water flows from the kitchen faucet or together with some other filter media in a filter assembly through which water is passed to improve its taste. In any case, the details of construction demand attention.
Consider, for example, a filter assembly configured for such applications as reverse osmosis water purification. The filter assembly may include a housing having an inlet, an outlet, and a passage arranged to communicate water from the inlet to the outlet, and the manufacturer might use an eight-inch length of one-inch inside diameter PVC tubing for the housing, with the interior of the tubing serving as the passage. Suitable structure such as molded end caps attached to opposite ends of the tubing enclose the interior and define the inlet and outlet.
The housing contains a filter media within the passage, such as granular activated carbon. The manufacturer mounts two filter elements on the housing at opposite ends of the activated carbon where they filter particulate matter and act as barriers to the activated carbon, confining it axially to a compact volume. Sandwiched between the two filter elements in that way, the activated carbon adsorbs substances from the water to improve its taste as the water flows through the filter assembly--flowing into the inlet, through the first filter element into the activated carbon, through the activated carbon to the second filter element, and thereafter through the second filter element and out of the outlet.
There are some problems with the filter elements, however. The porous member, for example, may take the form of a one-inch diameter disk that the manufacturer has cut from a sheet of suitable material, such as the spun bonded polypropolene commercially available under the tradename "TYPAR" or "REEMAY," and the support structure may take the form of a plastic ring to which the manufacturer has glued the periphery of the disk. So configured, the resulting filter element looks something like a flat, paper-thin diaphragm stretched across the plastic ring, a structure having certain drawbacks that need to be overcome.
Picture two such filter elements installed in an activated carbon filter assembly at opposite ends of a body of activated carbon. In those positions, the porous disk of each filter element should have a relatively large surface area in order to avoid a high pressure drop across the disk. But it should have a relatively small cross sectional area so that the activated carbon will have a favorable length to diameter ratio for filtering purposes.
Other considerations are just as conflicting. The diameter of the disk should be kept relatively small so that the disk does not deform or bulge axially because that can allow the activated carbon to loosen or shake with resulting voids or channeling. However, the diameter should be relatively large to offset the effect of those portions of the granular activated carbon called "fines," the fines including very fine particles which can abut the disk and result in a somewhat reduced effective filter element surface area. In addition, the glue at the periphery of the disk covers some of the actual filter element surface area so that it further reduces the effective filter element surface area.
Thus, it is desirable to have an improved filter element, assembly, and fabrication method that better alleviate those concerns.